In a standard schema based database, a one-to-many relationship may be implemented where a single document (parent) is related to zero, one or more other documents (children) within the database. This allows for information common to many documents to be represented in one place, rather than being repeated for each document. This results in lower storage needs as well as the ability to modify the common information once, rather than in every document to which it relates.
A schemaless database stores and retrieves data using data models other than strict tabular relations which are generally required in standard schema based databases. As a result, schemaless databases offer greater simplicity of design, greater horizontal scaling and finer control over availability. The schemaless database is often a highly optimized key-value type of storage intended for simple retrieval and appended operation. This type of storage provides significant performance benefits in terms of minimizing latency and increasing throughput. The schemaless database is timing increasing use in the big-data and in web application industries were this type of performance is necessary.
However, a schemaless database does have certain limitation compared to standard schema database which inherently implements tabular relations. In a standard schemaless database, a document consists of one or more key-value pairs that are stored in a collection database. A document has an identification (ID) string which uniquely identifies the document within a collection. However, due to the technology limitations of a schemaless database, while a collection may contain one or more documents, it cannot contain other collections. As a result, it is not possible to relate documents in a one-to-many relationship.
Therefore, the problem with schemaless databases is that they do not provide for nested relationships between documents stored within one or more collections.